This invention relates generally to electrical connectors and, more particularly, to an electrical connector for use in the transmission of high frequency signals.
Data communication networks are being developed which enable the flow of information to ever greater numbers of users at ever higher transmission rates. A problem is created, however, when data is transmitted at high rates over a plurality of circuits of the type that comprise multi-pair data communication cable. In particular, at high transmission rates, each wiring circuit itself both transmits and receives electromagnetic radiation so that the signals flowing through one circuit or wire pair (the xe2x80x9csource circuitxe2x80x9d) may couple with the signals flowing through another wire pair (the xe2x80x9cvictim circuitxe2x80x9d). The unintended electromagnetic coupling of signals between different pairs of conductors of different electrical circuits is called crosstalk and is a source of interference that often adversely affects the processing of these signals. The problem of crosstalk in information networks increases as the frequency of the transmitted signals increases.
In the case of local area network (LAN) systems employing electrically distinct twisted wire pairs, crosstalk occurs when signal energy inadvertently xe2x80x9ccrossesxe2x80x9d from one signal pair to another. The point at which the signal crosses or couples from one set of wires to another may be 1) within the connector or internal circuitry of the transmitting station, referred to as xe2x80x9cnear-endxe2x80x9d crosstalk, 2) within the connector or internal circuitry of the receiving station, referred to as xe2x80x9cear-end crosstalkxe2x80x9d, or 3) within the interconnecting cable.
Near-end crosstalk (xe2x80x9cNEXTxe2x80x9d) is especially troublesome in the case of telecommunication connectors of the type specified in sub-part F of FCC part 68.500, commonly referred to as modular connectors. Such modular connectors include modular plugs and modular jacks. The EIA/TIA of ANSI has promulgated electrical specifications for near-end crosstalk isolation in network connectors to ensure that the connectors themselves do not compromise the overall performance of the unshielded twisted pair interconnect hardware typically used in LAN systems. The EIA/TIA Category 5 electrical specifications specify the minimum near-end crosstalk isolation for connectors used in 100 ohm unshielded twisted pair Ethernet type interconnects at speeds of up to 100 MHz.
While it is desirable to use modular connectors for data transmission for reasons of economy, convenience and standardization, the standard construction of modular jacks inherently results in substantial rear-end crosstalk at high frequency operation. In particular, conventional modular jacks generally comprise a plurality of identically configured contact/terminal wires that extend parallel and closely spaced to each other thereby creating the possibility of excessive near-end crosstalk at high frequencies.
High speed data transmission cable typically comprise four circuits defined by eight wires arranged in four twisted pairs. The cable is typically terminated by modular plugs having eight contacts, and specified ones of the four pairs of the plug contacts are assigned to terminate respective specified ones of the four cable wire pairs according to ANSI/EIA/TIA standard 568 . The four pairs of plug contacts in turn engage four corresponding pairs of jack contacts. In particular, the standard 568 contact assignment for the wire pair designated xe2x80x9c1xe2x80x9d is the pair of plug and jack contacts located at the 4-5 contact positions. The cable wires of the pair designated xe2x80x9c3xe2x80x9d are, according to standard 568 , terminated by the plug and jack contacts located at the 3-6 positions which straddle the xe2x80x9c4-5xe2x80x9d plug and jack contacts that terminate wire pair xe2x80x9c1xe2x80x9d. Near-end crosstalk between wire pairs xe2x80x9c1xe2x80x9d and xe2x80x9c3xe2x80x9d during high speed data transmission has been found to be particularly troublesome in connectors that terminate cable according to standard 568.
When crosstalk occurs between electrically distinct circuits that are separated by a distance of much less than one wavelength, signal energy is transferred from one circuit to another either through inductive coupling capacitive coupling, or a combination of the two. For Category 5 interconnects, the shortest wavelength of interest is 3 meters, corresponding to the highest frequency of operation, 100 MHz. Since connector contact spacing in Category 5 connectors is much less than 3 meters, capacitive (electric field) and/or inductive (magnetic field) coupling will be responsible for measurable crosstalk within the connector.
Capacitive coupling will dominate when:
1) source circuits switch large voltages very quickly (large dv/dt) and/or operate at relatively high impedance levels ( greater than  greater than 1 kxcexa9);
2) source and/or victim circuits have large surface areas (wide long conductors); and
3) source and victim circuits are closely spaced and separated by dielectrics (nonconductors) that increase mutual capacitance between the source and victim circuits.
Inductive coupling will dominate when:
1) source circuits switch large currents very quickly (large di/dt) and/or operate at relatively high impedance levels ( less than  less than 100xcexa9);
2) source and/or victim circuits enclose large loop areas; and
3) source and victim circuits are closely spaced and have their current loops oriented along parallel axes.
Accordingly, it is an object of the present invention to provide new and improved connectors for use in data transmission at high frequencies.
Another object of the present invention is to provide new and improved high frequency connectors which reduce near-end crosstalk.
Still another object of the present invention is to provide new and improved modular connectors which reduce near-end crosstalk.
A still further object of the present invention is to provide new and improved high frequency electrical connectors which reduce near-end crosstalk and which are simple and inexpensive in construction.
Yet another object of the present invention is to provide new and improved modular jacks which reduce near-end crosstalk when connected to modular plugs that terminate high speed data transmission cable according to ANSI/EIA/TIA standard 568 .
Briefly, these and other objects are attained by modifying the standard construction of modular jacks, which generally comprise a plurality of identically configured contact/terminal wires, by providing one of at least one of the pairs of the jack contact/terminal wires that terminate respective cable wire signal pairs with a geometrical configuration that differs from the configuration of the other contact/terminal wire terminating that cable wire signal pair. In this manner, capacitive coupling is reduced by reducing the total surface area that is capable of storing charge between contact pairs, and inductive coupling is reduced by reducing magnetic field coupling between signal pairs by using asymmetrical contact pairs to tilt the axis of the contact pair""s loop current, i.e. by tilting or skewing the path in which the signal current flows through the contact pair.
In a preferred embodiment, the modular jack has a plurality of contact/terminal wires, each of which defines a contact, a pin-like terminal, and a conductor portion interconnecting the contact and terminal. The contact/terminal wires of a first set each have a xe2x80x9crearward facingxe2x80x9d configuration, i.e., the free end of the jack contact faces toward the closed end of the jack with the respective jack terminal being interconnected to the contact at the region of the open end of the jack so that signals transmitted through the contact flow toward the open end of the jack. In accordance with the invention, the jack is provided with a second set of contact/terminal wires, each of which is configured to define a jack contact that xe2x80x9cfaces forwardlyxe2x80x9d, i.e., the free end of the jack contact faces toward the open end of the jack with the respective jack terminal being interconnected to the contact at the region of the closed end of the jack. Signals transmitted through the contacts of the second set flow toward the closed end of the jack, i.e., in a direction substantially opposite to the direction in which the signals flow through the contacts of the first set.
In the case of an eight contact, eight position modular jack adapted for connection to a modular plug terminating an eight wire (four signal pairs) cable in accordance with the wire-contact assignments specified by ANSI/EIA/TIA standard 568, near-end crosstalk is reduced to a substantial extent by providing the pairs of contact/terminal wires assigned to terminate wire or signal pairs xe2x80x9c1xe2x80x9d and xe2x80x9c3xe2x80x9d with asymmetrical configurations. Specifically, the contact/terminal wires at positions 4 and 5 which terminate wire pair xe2x80x9c1xe2x80x9d have asymmetrical configurations, while the contact/terminal wires at positions 3 and 6 which terminate wire pair xe2x80x9c3xe2x80x9d have asymmetrical configurations.